Method and apparatus of configuring downlink timing and transmitting random access response in mobile communication system using carrier aggregation

ABSTRACT

A method of configuring downlink timings and transmitting a random access response message is provided for a random access procedure in a Long Term Evolution (LTE) system supporting carrier aggregation. The method for adjusting timing of a terminal in a wireless communication system supporting carrier aggregation of at least one carrier includes transmitting a Random Access Preamble to a base station, and receiving a Random Access Response with a Timing Advance Command (TAC) for commanding uplink timing adjustment from the base station, wherein the Random Access Response comprises information indicating a Timing Advance Group (TAG) to which the TAC is applied.

PRIORITY

This application is a continuation application of prior application Ser.No. 15/439,512, filed on Feb. 22, 2017, which is a continuationapplication of prior application Ser. No. 14/602,630, filed on Jan. 22,2015, which has issued as U.S. Pat. No. 9,585,188 on Feb. 28, 2017,which is a continuation of prior application Ser. No. 13/440,195, filedon Apr. 5, 2012, which has issued as U.S. Pat. No. 8,964,793 on Feb. 24,2015, which claims the benefit under 35 U.S.C. § 119(e) of a U.S.Provisional application filed on Apr. 5, 2011 in the U.S. Patent andTrademark Office and assigned Ser. No. 61/471,872, and which claimed thebenefit under 35 U.S.C § 119(a) of a Korean patent application filed onApr. 5, 2012 in the Korean Intellectual Property Office and assignedSerial number 10-2012-0035216, the entire disclosure of each of which ishereby incorporated by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a radio communication system. Moreparticularly, the present invention relates to a method of configuringdownlink timings and transmitting a random access response message inrandom access procedure in a Long Term Evolution (LTE) system supportingcarrier aggregation.

2. Description of the Related Art

With the rapid advance of radio communication technology, communicationsystems have significantly evolved. LTE is one of the promising 4^(th)generation mobile communication technologies. In an LTE system, varioustechniques are adopted to meet the explosively increasing trafficdemands, and carrier aggregation is one of such techniques. Carrieraggregation is used to flexibly expand available bandwidth byaggregating multiple secondary carriers with a primary carrier, unlikethe legacy LTE system using a single carrier, between a User Equipment(UE) and an evolved Node B (eNB). In LTE, the primary carrier isreferred to as primary cell (PCell) and the secondary carrier assecondary cell (SCell).

In a case where the locations of the eNB apparatuses using the primaryand secondary carriers are different from each other due to thedeployment of repeaters and Remote Radio Head, the uplink transmissiontiming may need to be changed. For example, when the eNB apparatusoperating with the primary carrier and another eNB apparatus operatingwith the secondary carrier are located at different places, it may causea problem in transmission timing according to the location of the UEsince the uplink signal to the eNB apparatus located at a greaterdistance should be transmitted earlier than the signal to the other eNBapparatus.

In this case, i.e., when multiple uplink timings exist, referencesignals for the respective uplink timings may need to be transmitted.There is therefore a need of defining a rule for determining the cell ofwhich downlink signal is configured to carry Downlink Timing ReferenceSignal.

Furthermore, the current standard specification has no definition on theinformation for indicating the carrier on which the preamble has beentransmitted by the UE in the random access response message, the randomaccess response message carrying the uplink timing information in therandom access procedure for acquiring actual uplink timing.

Therefore, a need exists to define the information for indicating thecarrier on which the preamble has been transmitted by the UE in therandom access response message.

SUMMARY OF THE INVENTION

Aspects of the present invention are to address at least theabove-mentioned problems and/or disadvantages and to provide at leastthe advantages described below. Accordingly, an aspect of the presentinvention is to provide a method for transmitting a message includingthe information on the downlink signal to be referenced as the downlinktiming reference signal and the information on the cell with which thetiming indicated in the timing advance information transmitted by theevolved Node B (eNB) for adjusting the uplink timing in the randomaccess procedure, in the wireless communication system adopting thecarrier aggregation technique.

Another aspect of the present invention is to provide a method forconfiguring a downlink reference cell for a carrier group in thewireless communication system operating adopting carrier aggregationtechnique operating with multiple uplink transmission timings forrespective carrier groups. In addition, an exemplary embodiment of thepresent invention defines a Random Access Response message transmittedby the eNB in a random access procedure to acquire synchronization ofuplink transmission timing in a specific carrier group.

In accordance with an aspect of the present invention, a method foradjusting timing of a terminal in a wireless communication systemsupporting carrier aggregation of at least one carrier is provided. Themethod includes transmitting a Random Access Preamble to a base station,and receiving a Random Access Response with a Timing Advance Command(TAC) for commanding uplink timing adjustment from the base station,wherein the Random Access Response comprises information indicating aTiming Advance Group (TAG) to which the TAC is applied.

In accordance with another aspect of the present invention, a method foradjusting timing of a base station in a wireless communication systemsupporting carrier aggregation of at least one carrier is provided. Themethod includes receiving a Random Access Preamble from a terminal, andtransmitting a Random Access Response with a TAC for commanding uplinktiming adjustment to the terminal, wherein the Random Access Responsecomprises information indicating a TAG to which the TAC is applied.

In accordance with another aspect of the present invention, a terminalfor adjusting transmission/reception timing of a signal in a wirelesscommunication system supporting carrier aggregation of at least onecarrier is provided. The terminal includes a transceiver forcommunicating signals with a base station, and a controller fortransmitting a Random Access Preamble to a base station and forreceiving a Random Access Response with a TAC for commanding uplinktiming adjustment from the base station, wherein the Random AccessResponse comprises information indicating a TAG to which the TAC isapplied.

In accordance with another aspect of the present invention, a basestation for adjusting transmission/reception timing of a signal in awireless communication system supporting carrier aggregation of at leastone carrier is provided. The base station includes a transceiver forcommunicating signals with a terminal, and a controller for receiving aRandom Access Preamble from a terminal and for transmitting a RandomAccess Response with a TAC for commanding uplink timing adjustment tothe terminal, wherein the Random Access Response comprises informationindicating a TAG to which the TAC is applied.

Other aspects, advantages, and salient features of the invention willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainexemplary embodiments of the present invention will be more apparentfrom the following description taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is a diagram illustrating an architecture of a Long TermEvolution (LTE) system according to an exemplary embodiment of thepresent invention;

FIG. 2 is a diagram illustrating a protocol stack of an LTE systemaccording to an exemplary embodiment of the present invention;

FIG. 3 is a diagram illustrating carrier aggregation in an LTE systemaccording to an exemplary embodiment of the present invention;

FIG. 4 is a diagram illustrating a principle of uplink timingsynchronization in an Orthogonal Frequency Division Multiplexing(OFDM)-based 3^(rd) Generation Partnership Project (3GPP) LTE systemaccording to an exemplary embodiment of the present invention;

FIG. 5 is a diagram illustrating an exemplary network environment havingnetwork entities operating on primary and secondary carriers atdifferent locations in a system supporting carrier aggregation accordingto an exemplary embodiment of the present invention;

FIG. 6 is a diagram illustrating signal flows between an evolved Node B(eNB) and a User Equipment (UE) according to an exemplary embodiment ofthe present invention;

FIG. 7 is a flowchart illustrating a UE procedure of a transmissiontiming configuration method according to an exemplary embodiment of thepresent invention;

FIG. 8 is a flowchart illustrating an eNB procedure of a transmissiontiming configuration method according to an exemplary embodiment of thepresent invention;

FIGS. 9A-9E illustrate formats of a Random Access Response (RAR) andTiming Advance Command (TAC) Medium Access Control (MAC) Control Element(CE) messages according to exemplary embodiments of the presentinvention;

FIG. 10 is a block diagram illustrating a configuration of a UEaccording to an exemplary embodiment of the present invention; and

FIG. 11 is a block diagram illustrating a configuration of an eNBaccording to an exemplary embodiment of the present invention.

Throughout the drawings, it should be noted that like reference numbersare used to depict the same or similar elements, features, andstructures.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of exemplaryembodiments of the invention as defined by the claims and theirequivalents. It includes various specific details to assist in thatunderstanding but these are to be regarded as merely exemplary.Accordingly, those of ordinary skill in the art will recognize thatvarious changes and modifications of the embodiments described hereincan be made without departing from the scope and spirit of theinvention. In addition, descriptions of well-known functions andconstructions may be omitted for clarity and conciseness.

The terms and words used in the following description and claims are notlimited to the bibliographical meanings, but, are merely used by theinventor to enable a clear and consistent understanding of theinvention. Accordingly, it should be apparent to those skilled in theart that the following description of exemplary embodiments of thepresent invention is provided for illustration purpose only and not forthe purpose of limiting the invention as defined by the appended claimsand their equivalents.

It is to be understood that the singular forms “a,” “an,” and “the”include plural referents unless the context clearly dictates otherwise.Thus, for example, reference to “a component surface” includes referenceto one or more of such surfaces.

By the term “substantially” it is meant that the recited characteristic,parameter, or value need not be achieved exactly, but that deviations orvariations, including for example, tolerances, measurement error,measurement accuracy limitations and other factors known to those ofskill in the art, may occur in amounts that do not preclude the effectthe characteristic was intended to provide.

Exemplary embodiments of the present invention relate to a method and anapparatus for a User Equipment (UE) supporting carrier aggregation toactivate secondary carriers.

FIGS. 1 through 11, discussed below, and the various exemplaryembodiments used to describe the principles of the present disclosure inthis patent document are by way of illustration only and should not beconstrued in any way that would limit the scope of the disclosure. Thoseskilled in the art will understand that the principles of the presentdisclosure may be implemented in any suitably arranged communicationssystem. The terms used to describe various embodiments are exemplary. Itshould be understood that these are provided to merely aid theunderstanding of the description, and that their use and definitions inno way limit the scope of the invention. Terms first, second, and thelike are used to differentiate between objects having the sameterminology and are in no way intended to represent a chronologicalorder, unless where explicitly stated otherwise. A set is defined as anon-empty set including at least one element.

FIG. 1 is a diagram illustrating an architecture of a Long TermEvolution (LTE) system according to an exemplary embodiment of thepresent invention.

Referring to FIG. 1, a radio access network of a mobile communicationsystem includes evolved Node Bs (eNBs) 105, 110, 115, and 120, aMobility Management Entity (MME) 125, and a Serving-Gateway (S-GW) 130.The UE 135 connects to an external network via eNBs 105, 110, 115, and120 and the S-GW 130.

In FIG. 1, the eNBs 105, 110, 115, and 120 correspond to legacy node Bsof Universal Mobile Communications System (UMTS). The eNBs 105, 110,115, and 120 allow the UE to establish a radio link and are responsiblefor complicated functions as compared to the legacy node B. In the LTEsystem, all the user traffic including real time services, such as Voiceover Internet Protocol (VoIP), are provided through a shared channel andthus there is a need for a device which is located in the eNB toschedule data based on the state information, such as UE bufferconditions, power headroom state, channel state, and the like.

Typically, one eNB controls a plurality of cells. In order to secure thedata rate of up to 100 Mbps, the LTE system adopts Orthogonal FrequencyDivision Multiplexing (OFDM) as a radio access technology. In addition,the LTE system adopts Adaptive Modulation and Coding (AMC) to determinethe modulation scheme and channel coding rate in adaptation to thechannel condition of the UE.

The S-GW 130 is an entity to provide data bearers so as to establish andrelease data bearers under the control of the MME 125. MME 125 isresponsible for various control functions and connected to a pluralityof eNBs 105, 110, 115, and 120.

FIG. 2 is a diagram illustrating a protocol stack of an LTE systemaccording to an exemplary embodiment of the present invention.

Referring to FIG. 2, the protocol stack of the LTE system includesPacket Data Convergence Protocol (PDCP) 205 and 240, Radio Link Control(RLC) 210 and 235, Medium Access Control (MAC) 215 and 230, and Physical(PHY) 220 and 225.

The PDCP 205 and 240 is responsible for IP headercompression/decompression, and the RLC 210 and 235 is responsible forsegmenting the PDCP Protocol Data Unit (PDU) into segments inappropriate size for Automatic Repeat Request (ARQ) operation. ARQ isthe technique for determining whether the transmitted packet issuccessfully received and retransmitting the packets receivederroneously.

The MAC 215 and 230 is responsible for establishing connection to aplurality of RLC entities so as to multiplex the RLC PDUs into MAC PDUsand demultiplex the MAC PDUs into RLC PDUs.

The PHY 220 and 225 performs channel coding on the MAC PDU and modulatesthe MAC PDU into OFDM symbols to transmit over radio channel or performsdemodulating and channel-decoding on the received OFDM symbols anddelivers the decoded data to the higher layer. In addition, the PHYlayer uses Hybrid ARQ (HARQ) for additional error correction bytransmitting 1 bit information indicating for positive or negativeacknowledgement from the receiver to the transmitter. This is referredto as HARQ (ACKnowledgement/Non-ACKnowledgement) ACK/NACK information.

FIG. 3 is a diagram illustrating carrier aggregation in an LTE systemaccording to an exemplary embodiment of the present invention.

Referring to FIG. 3, typically, an eNB may use multiple carrierstransmitted and received in different frequency bands. For example, aneNB 305 can be configured to use carrier 315 with center frequency f1and carrier 310 with center frequency f3. If carrier aggregation is notsupported, the UE 330 has to transmit/receive data unit from one of thecarriers 310 and 315. However, the UE 330 having the carrier aggregationcapability can transmit/receive data using both the carriers 310 and315. The eNB can increase the amount of the resource to be allocated tothe UE having the carrier aggregation capability in adaptation to thechannel condition of the UE so as to improve the data rate of the UE.

In a case where a cell is configured with one downlink carrier and oneuplink carrier as a concept of the related art, the carrier aggregationcan be understood as if the UE communicates data via multiple cells.With the use of carrier aggregation, the maximum data rate increases inproportion to the number of aggregated carriers.

In the following description, the phrase “the UE receives data through acertain downlink carrier or transmits data through a certain uplinkcarrier” means to transmit or receive data through control and datachannels provided in a cell corresponding to center frequencies andfrequency bands of the downlink and uplink carriers. Although thedescription is directed to an LTE mobile communication system forexplanation convenience, exemplary embodiments of the present inventioncan be applied to other types of wireless communication systemssupporting carrier aggregation.

FIG. 4 is a diagram illustrating a principle of uplink timingsynchronization in an OFDM-based 3^(rd) Generation Partnership Project(3GPP) LTE system according to an exemplary embodiment of the presentinvention.

Referring to FIG. 4, an exemplary case where the UE #1 is located nearthe eNB while the UE #2 is located far from the eNB is illustrated. InFIG. 4, T_pro1 indicates the first propagation delay time to the UE #1,and T_pro2 indicates the second propagation delay to the UE #2.

As shown in FIG. 4, the UE #1 is located near the eNB as compared to theUE #2 and thus has a relatively short propagation delay (i.e., T_pro1 is0.334 μs, whereas T_pro2 is 3.33 μs).

When the UE #1 and UE #2 power on or in idle mode within a cell of theeNB, the uplink timing of the UE #1, uplink timing of the UE #2, anduplink timings of other UEs detected by the eNB in the cell may fail insynchronization.

Reference number 401 denotes uplink OFDM symbol transmission timing ofthe UE #1, and reference number 403 denotes uplink OFDM symboltransmission timing of the UE #2. By taking notice of the uplinktransmission propagation delays of the UE #1 and UE #2, the eNB mayreceive the uplink OFDM symbols at the timings as denoted by referencenumbers 407 and 409.

The UE #1's uplink symbol transmitted at the timing 401 is received bythe eNB at the timing 407 with propagation delay while the UE #2'suplink symbol transmitted at the timing 403 is received by the eNB atthe timing 409 with propagation delay. In FIG. 4, since the timings 407and 409 are before the synchronization is acquired between the uplinktransmission timings of the UE #1 and UE #2, the uplink OFDM symbolreception and decoding start timing 405 of the eNB, the UE #1's uplinkOFDM symbol reception timing 407, and the UE #2's uplink OFDM symbolreception timing 409 are different among each other.

In this case, the uplink symbols transmitted by the UE #1 and UE #2 haveno orthogonality so as to interfere with each other and, as aconsequence, the eNB is likely to fail decoding the uplink symbolstransmitted, at the timing 401 and 403, by the UE #1 and UE #2 due tothe interference and the mismatch between the uplink symbol receptiontimings 407 and 409.

Uplink timing synchronization is a procedure for acquiring the eNB'suplink symbol reception timings with the UE #1 and UE #2 and, if theuplink timing synchronization procedure completes, it is possible toacquire the synchronization among the eNB's uplink OFDM symbol receptionand decoding start timing, UE #1's uplink OFDM symbol reception timing,and UE #2's uplink OFDM symbol reception timing as denoted by referencenumbers 411, 413, and 415.

In the uplink timing synchronization procedure, the eNB transmits TimingAdvance (hereinafter, referred to as TA) information to the UEs tonotify of the timing adjustment amount.

The eNB can transmit the TA information in the Timing Advance CommenceMAC Control Element (TAC MAC CE) or in the Random Access Response (RAR)message in response to the random access preamble transmitted by the UEfor initial access.

The UE can adjust the uplink transmission timing based on the TAinformation. The UE starts a time alignment timer (timeAlignmentTimer orTAT) upon receipt of TA information, restarts the TAT in response toadditional TA reception, and invalidates the TA upon expiry of the TA tostop uplink communication with the corresponding eNB.

By acquiring the synchronization among the transmission timings asdescribed above, it is possible to maintain the orthogonality betweenthe uplink symbols of the UE #1 and UE #2 such that the eNB cansuccessfully decode the uplink symbols from the UE #1 and UE #2 at thetimings 401 and 403.

FIG. 5 is a diagram illustrating an exemplary network environment havingnetwork entities operating on primary and secondary carriers atdifferent locations in a system supporting carrier aggregation accordingto an exemplary embodiment of the present invention.

Referring to FIG. 5, Remote Radio Heads (RRHs) 503 operating onfrequency band F2 507 are around macro eNB 501 using frequency band F1505. If the UE is connected to both the macro eNB and RRH and locatednear the RRH and if the UE transmits a signal via the RRH, the signalcan reach the RRH at an appropriate timing even when there is a littledelay due to the short distance. However, the signal transmitted to themacro eNB fails to reach the macro eNB at appropriate timing due to thelong distance. In order to address this problem, the UE operating withaggregated carriers may need to synchronize multiple uplink transmissiontimings.

For this purpose, an exemplary embodiment of the present inventionproposes a method in that the eNB categorizes the carriers havingsimilar uplink timings into a group to manage the carriers efficiently.This technique is referred to as Timing Advance Group (hereinafter,referred to as TAG).

In an exemplary case where one PCell (or first cell) and three SCells A,B and C (or second cells) exist, if the PCell and the SCell A havesimilar uplink timings, they can be categorized into group 1 while theSCell B and SCell C are categorized into group 2.

In this case, the eNB transmits the TA information to the group 1 in theTAC MAC CE or RAR to command uplink timing adjustment such that the UEadjusts uplink timings of both the PCell and SCell A based on theinformation carried in the TAC MAC CE. The TAG including the PCell isreferred to as PTAG, and the TAG including no PCell is referred to asSTAG.

When multiple uplink timings are used, a reference downlink cell for theuplink timing information, i.e., TA information, may need to bedetermined. In FIG. 5, if the UE is connected to both the macro eNB andthe RRH at a location close to the RRH, the downlink signal from the RRHarrives earlier than the downlink signal from the macro eNB. In thissituation, if the eNB transmits TA information for adjusting uplinktiming of the UE, it may be necessary to define how to determine thesignal to be referred for adjusting the timing. That is, in uplinktransmission through a SCell belonging to STAG, if the TA information isreceived from the eNB, there is a problem on how to select/configure thedownlink timing reference cell as the reference of the TA informationfor adjusting uplink timing.

Furthermore, when the TA information is received, there is anotherproblem to determine the TAG to which the TA information is applied foruplink transmission. In a case where multiple TA configurations may beneeded for multiple TAGs as aforementioned, if the TA configuration isgenerated per TAG, the uplink transmission delay increases in proportionto the number of TAG.

A description is made of the method for overcoming the aforementionedproblems of the prior arts with reference to FIG. 6.

FIG. 6 is a diagram illustrating signal flows between an eNB and a UEaccording to an exemplary embodiment of the present invention.

Referring to FIG. 6, the eNB has three cells 603, 605, and 607, and theUE 601 is connected to the eNB through the cell 607. Here, the cell 607is the PCell of the UE. As above described, the PCell denotes theprimary carrier of the UE. The eNB is aware of the UE's carrieraggregation capability and sends the UE 601 a Radio Resource Control(RRC) layer message including information on the SCells aggregated forthe UE (SCell 1 and SCell 2 in FIG. 6), STAG information (SCell 1 andSCell 2 belong to STAG 1), and TAT information on the TAG at step 611.

The RRC layer message can be the RRCConnectionReconfiguration message.FIG. 6 is directed to an exemplary case where the RRC layer messageincludes the Random Access Channel (RACH) configuration information ofthe SCell 1 603 but not the RACH configuration information of the SCell2 605. If the eNB requests the UE 601 to transmit Random Access Preamblethrough the RACH of the SCell 1 afterward, the UE 601 transmits theRandom Access Preamble using the RACH configuration information retainedin the SCell 1 603. Since the Random Access Preamble has beentransmitted through the RACH of the SCell 1 603, the STAG1's TAinformation received since then is applied to the downlink timing of theSCell 1 through which the Random Access Preamble has been transmitted toadjust the uplink transmission timing of the SCell 2 605 as well as theuplink transmission timing of the SCell 1 603. That is, the referencedownlink timing for adjusting the uplink timings of the SCells (i.e.,SCell 1 and SCell 2) belonging to an STAG is configured as the downlinktiming of the SCell 1 603 through which the Random Access is performedwith the RACH configuration information. If the RRC layer message isreceived, the UE transmits an RRC layer acknowledgement message at step613. The RRC layer acknowledgement message can be theRRCConnectionReconfigurationComplete message.

Thereafter, the eNB transmits an Activation/deactivation MAC Control CE(Activation/deactivation MAC CE) to the UE 601 to activate the addedSCell 1 603 and SCell 2 605 at step 615. Thereafter, the eNB transmits aPhysical Downlink Control Channel (PDCCH) order to request the UE totransmit the Random Access Preamble through a specific cell (SCell 1 inFIG. 6) at step 617.

Upon receipt of the PDCCH order, the UE 601 transmits the Random AccessPreamble through the cell indicated by the PDCCH order (SCell 1 in FIG.6) at step 619. If the Random Access Preamble is received, the eNBtransmits the proposed Random Access Response (RAR) including the TAinformation by referencing the downlink signal of the cell (SCell 1 inFIG. 6) having the RACH through which the Random Access Preamble isreceived at step 621. The RAR message includes a TAG identifier (TAG ID)to indicate the uplink timings of the TAG to be adjusted or the TAinformation of a plurality of TAGS. A description is made of the formatof the RAR message later with reference to FIG. 9. If the RAR message isreceived, the UE determines the TAG ID and TA information, or TAinformation per TAG ID, to adjust the uplink transmission timings of thecells belonging to the TAG identified by the TAG ID at step 623.

Thereafter, if the eNB can request the UE to retransmit the preamble andthus the UE retransmits the preamble in response to the request, the eNBcan adjust the uplink transmission timings of the cells belonging to aspecific TAG or the uplink timings of the cells belonging to multipleTAGs using the new RAR message or the new TAC MAC CE message at step625. That is, in this exemplary embodiment operating with PTAG and STAG1, the TAG ID (i.e., PTAG or STAG 1) is included in the new RAR messageor the TAC MAC CE message to adjust the uplink transmission timings ofthe cells belonging to the TAG at step 627. A description is made of theformat of the new TAC MAC CE message with reference to FIG. 9.

FIG. 7 is a flowchart illustrating a UE procedure of a transmissiontiming configuration method according to an exemplary embodiment of thepresent invention.

Referring to FIG. 7, the UE receives a carrier aggregation-relatedmessage transmitted by the eNB at step 703, the message including theinformation on the carriers available for the UE and the information onthe group of carriers that can be configured with the same timingadvance. Thereafter, the UE receives a message instructing activation ofa specific cell at step 704. This message can be theActivation/deactivation MAC CE message. The UE then receives a PDCCHorder transmitted by the eNB at step 705, the PDCCH order instructingthe UE to transmit a preamble through a specific cell (PCell or SCell).The UE transmits a Random Access Preamble through the cell indicated bythe PDCCH order at step 707.

Thereafter, the UE receives a Random Access Response (RAR) messagetransmitted by the eNB at step 709. In an exemplary embodiment of thepresent invention, when the same Random Access Preamble is transmittedthrough different cells at the same timing, an RAR message including TAGID is proposed to discriminate among the cells such that the eNB cancommand the adjustment of the uplink timing of the cell belonging to theTAG and indicated by the TAG ID. For example, in the case of FIG. 6, apreamble N is transmitted through both the SCell 1 and PCell at the sametiming and if the RAR message is transmitted through PCell, it becomesambiguous to determine whether the RAR message is the replay in responseto the preamble N transmitted through the SCell 1 or the PCell. In orderto address this ambiguity, an exemplary embodiment of the presentinvention proposes the RAR message including TAG ID (of PTAG or STAG 1in this embodiment). If the RAR message includes the timing advanceinformation and the TAG ID indicating the STAG1, the UE adjusts theuplink timing by referencing the downlink of the SCell 1 based on thetiming advance information carried in the RAR message.

Although not described in this exemplary embodiment, the RAR message canbe configured to include a plurality of TA information without extra TAGID. In this case, the uplink timings of the cells corresponding to therespective TAG can be adjusted according to the individual TAinformation included in the RAR message at step 711. That is, it isproposed to transmit the RAR message including the timing advanceinformation of the respective TAGs without additional TAG identifiersuch that the UE adjusts the uplink timings of the cell belonging to therespective TAGs, under the assumption that the eNB knows the uplinktimings of the respective TAGs.

Assuming that there are group 1 and group 2 and the eNB knows thedifference Δ of the timing advances of the group 1 and group 2, if thepreamble is received through a cell of the group 2, the timing advanceinformation of the group 1 (e.g., TA2−Δ) and the timing advanceinformation of the group 2 (e.g., TA2) are transmitted.

An exemplary embodiment of the present invention proposes a method inwhich the UE received the RAR configures the transmission timings byreferencing the downlink of the cell through the Random Access Preambleis transmitted at step 707 and configures the uplink transmissiontimings of the cells belonging to the TAG indicated by the RAR at step709.

In a case of STAG 1 of FIG. 6, if the eNB selects one of the downlinkcells configured with the Random Access Channel (RACH) configuration forrandom access among the SCell 1 and SCell 2 (SCell 1 in FIG. 6) andcommands the UE to transmit the Random Access Preamble.

Thereafter, the UE transmits the Random Access Preamble as indicated bythe RACH configuration information retained in the SCell 1 and, sincethe Random Access Preamble has been transmitted through the RACHconfigured with the SCell 1, the STAG1's TA information receivedafterward, is applied to for the downlink timing of the SCell 1 throughwhich the Random Access Preamble has been transmitted so as to adjustthe uplink transmission timing of the SCell 2 as well as the uplinktransmission timing of the SCell 1.

That is, an exemplary embodiment of the present invention proposes amethod in that the reference downlink timing for adjusting uplinktimings for the SCells belonging to an STAG (i.e., SCell 1 and SCell 2in FIG. 6) are configured to match the downlink timing of the SCell 1through which the random access procedure has been performed with theRACH configuration information and configure the uplink timing.

Thereafter, the UE starts a TAT of the corresponding TAG at step 713 andperforms uplink data transmission through the cell belonging to the TAGfor which the uplink synchronization has been acquired at step 715.

At step 717, the UE determines whether the RAR or TAC MAC CE for thecorresponding TAG is received. If the RAR or TAC MAC CE for thecorresponding TAG is received, the UE configures the downlink of thecell in which the preamble has been transmitted successfully as thereference cell among the SCells configured with RACH in thecorresponding TAB as at step 711 and adjusts the uplink timinginformation on the cells belonging to the TAG by referencing thedownlink reference cell at step 719. After adjusting the uplink timings,the UE restarts the TAT of the corresponding TAG at step 713 andperforms uplink data transmission through the corresponding cells atstep 715.

In contrast, if the RAR or TAC MAC CE is not received through the cellbelonging to the TAG, the UE determines whether the TAT of thecorresponding TAG has expired at step 721. If the TAT of thecorresponding TAG has expired, the UE terminates the procedure at step723 and, otherwise, continues uplink data transmission through thecorresponding cells at step 715.

FIG. 8 is a flowchart illustrating an eNB procedure of the transmissiontiming configuration method according to an exemplary embodiment of thepresent invention.

Referring to FIG. 8, the eNB configures SCells for a UE supportingcarrier aggregation with the STAG information including RACHconfiguration information at step 803. In order to activate theconfigured SCells, the eNB commands the user to activate the SCellsbelonging to a specific SCell by transmitting an Activation/deactivationMAC CE at step 805 and requests the UE to send the preamble for uplinktiming adjustment of the activated SCells by transmitting a PDCCH orderat step 807. If the UE transmits the preamble, the eNB receives thepreamble and transmits an RAR message including the TA informationgenerated based on the signal of the downlink cell selected as describedwith reference to FIGS. 6 and 7 at step 809. Here, the RAR message caninclude the ID of the STAG to which the activated SCell belongs or allthe TA information of other STAG and PTAG along with the STAG.Thereafter, the eNB allocates uplink resource to the UE in thecorresponding TAG and transmits data using the allocated resource atstep 811.

The UE determines whether it is necessary to further adjust the timingof the activated SCell at step 813. If it is necessary to further adjustthe timing of the activated SCell, the eNB transmits the RAR message orthe TAC MAC CE message to adjust the TA of the corresponding TAG at step815 and terminates the procedure at step 817. The TAC MAC CE can includethe TAG ID and TA information like the RAR message proposed in anexemplary embodiment of the present invention so as to adjust the uplinktiming of a specific TAG.

FIGS. 9A-9E illustrate formats of the RAR and TAC MAC CE messagesaccording to exemplary embodiments of the present invention.

Referring to FIG. 9A, a RAR message format according to the related artis illustrated. The RAR message of the related art includes a TimingAdvance Command field (11 bits) for adjusting uplink timing, a UL grantfield (20 bits) for indicating the location of the resource in themessage following the RAR message, a Temporary C-RNTI field (16 bits)for allocating temporary identifier to the UE attempting initial attachto the corresponding cell.

Referring to FIG. 9B, a format of the RAR message proposed in the firstexemplary embodiment of the present invention is illustrated. In thisexemplary embodiment, the Reserved (R) bit of the RAR message format ofthe related art is used as a TAG ID field which is set to 0 forindicating PTAG and 1 for indicating STAG 1.

Referring to FIG. 9C, a format of the RAR message proposed in the secondexemplary embodiment of the present invention is illustrated. In thisexemplary embodiment, the Reserved (R) field of the RAR message formatof the related art is used as a flag field which is set to 0 forindicating the use of RAR format of the related art (FIG. 9A) and 1 forindicating the TA of up to 4 TAGs.

Referring to FIG. 9D, a TAC MAC CE message format according to therelated is illustrated. The TAC MAC CE message of the related artincludes a 6-bit Timing Advance Command field for adjusting uplinktiming.

Referring to FIG. 9E, a format of the TAC MAC CE message according tothe first exemplary embodiment of the present invention is illustrated.In this exemplary embodiment, the two reserved (R) bits of the TAC MACCE message format of the related art are used as a TAG ID filed which isset to 00 for indicating PTAG, 01 for indicating STAG 1, 10 forindicating STAG 2, and 11 for indicating STAG 3 to adjust the uplinktiming of the TAG indicated by the TAG ID.

FIG. 10 is a block diagram illustrating a configuration of a UEaccording to an exemplary embodiment of the present invention.

Referring to FIG. 10, the UE transmits/receives data generated by ahigher layer device 1005 and controls messages generated by a controlmessage processor 1007. When transmitting a control signal and/or datato the eNB, the UE multiplexes the control signal and/or data by meansof the multiplexer/demultiplexer 1003 under the control of thecontroller 1009. When receiving control signal and/or data from the eNB,the UE receives the physical signal by means of the transceiver 1001,demultiplexes the received signal by means of themultiplexer/demultiplexer 1003, and delivers the demultiplexed signal tothe corresponding higher layer device 1005 or control message processor1007.

In this exemplary embodiment of the present invention, if the RRC layermessage, i.e., carrier aggregation configuration message, is received, acarrier aggregation processor 1011 determines a downlink timingreference cell according to one of the methods described with referenceto FIG. 6. Thereafter, if a preamble transmission command is receivedfrom the eNB, the controller 1009 transmits the preamble, receives anRAR message formatted according to the method proposed in FIG. 6 (seeFIG. 9) from the eNB, and adjusts, if the RAR message includes the TAGID and TA, the uplink timing of the TAG identified by the correspondingTAG and, adjusts, if the RAR message includes a plurality of TAinformation, the uplink timings of the corresponding TAGs at a time.Similarly, if the TAC MAC CE message is received from the eNB, thecontroller 1009 controls uplink timing of the corresponding TAGaccording to the information contained in the TAC MAC CE.

FIG. 11 is a block diagram illustrating a configuration of an eNBaccording to an exemplary embodiment of the present invention.

Referring to FIG. 11, the eNB transmits/receives data generated by ahigher layer device 1105 and controls messages generated by a controlmessage generator 1107. In a transmission mode, the data is multiplexedby a multiplexer/demultiplexer 1103 and transmitted through atransceiver 1101 under the control of a controller 1109. In a receptionmode, the physical signal is received by the transceiver 1101,demultiplexed by the multiplexer/demultiplexer 1103, and delivered tothe higher layer device 1105 or the control message processor 1107according to the message information under the control of the controller1109.

In this exemplary embodiment of the present invention, in order for acarrier aggregation processor 1111 to configure a specific SCell andSTAG for the UE, the control message processor 1107 transmits carrieraggregation configuration message as an RRC layer message. Thereafter,the controls message processor 1107 generates an Activation/deactivationMAC CE and transmits this message to the UE for activating a specificSCell and transmits a PDCCH order to request the UE to transmit thepreamble for acquiring uplink synchronization in the SCell. If thepreamble is received, the control message generator 1107 determines thedownlink reference signal according to one of the methods proposed inFIG. 6 and generates/transmits the RAR message including the TAinformation (see FIG. 9). If it is determined that the additional uplinktiming adjustment is required for the UE, the eNB generates a TAC MAC CEproposed in this exemplary embodiment of the present invention andtransmits the TAC MAC CE to the UE such that the UE adjusts the uplinktiming of the corresponding TAG.

As described above, the downlink timing configuration method andapparatus of exemplary embodiments of the present invention is capableof preventing the UE from malfunctioning by clearly defining thedownlink timing reference cell in the system supporting the carrieraggregation technique and operating with a plurality of uplink timingsand capable of guaranteeing reliable operation of the system byindicating the TAG of which uplink timing is to be adjusted using theuplink timing adjustment command.

As described above, the downlink timing configuration method andapparatus of exemplary embodiments of the present invention defines arule for determining the downlink signal to be referenced in the systemusing a plurality of uplink timings such that it is possible to adjustthe uplink timings accurately with error even when receiving the uplinktiming adjustment information.

While the invention has been shown and described with reference tocertain exemplary embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims and their equivalents.

What is claimed is:
 1. A method performed by a terminal in acommunication system, the method comprising: obtaining first timealignment timer (TAT) information for a first timing advance group(TAG), second TAT information for a second TAG, and information forconfiguring a secondary cell (SCell); receiving, from a base station, afirst medium access control (MAC) control element for activating theSCell; activating the SCell based on the first MAC control element;receiving, from the base station, a physical downlink control channel(PDCCH) order for the SCell activated based on the first MAC controlelement; transmitting, to the base station, a random access preamblebased on the PDCCH order; receiving, from the base station, a randomaccess response including timing advance information in response to atransmission of the random access preamble; applying the timing advanceinformation to a TAG including the SCell in case that the random accessresponse is received; and starting a TAT associated with the TAGincluding the SCell among the first TAT information and the second TATinformation in case that the random access response is received, whereinthe TAT associated with the TAG is used to control how long the terminalconsiders at least one cell included in the TAG to be uplink aligned. 2.The method of claim 1, further comprising: receiving, from the basestation, a second MAC control element including an identity of the TAGincluding the SCell, and a timing advance command (TAC) for the TAGincluding the SCell; applying the TAC to the TAG including the SCell incase that the second MAC control element is received; and restarting theTAT associated with the TAG including the SCell among the first TATinformation and the second TAT information in case that the second MACcontrol element is received.
 3. The method of claim 2, wherein theidentity of the TAG is set to 0, if the TAG is a primary TAG including aprimary cell (PCell), and wherein the identity of the TAG is set to avalue other than 0 if the TAG is not a primary TAG.
 4. The method ofclaim 2, wherein a length of a field of the identity is 2 bits and alength of a field of the TAC is 6 bits.
 5. The method of claim 1,wherein the random access preamble is transmitted on the SCell based ona random access channel (RACH) configuration information for the SCell,wherein the random access response is received on a Pcell, and whereinuplink transmission on the SCell is performed based on the timingadvance information.
 6. A terminal in a communication system, theterminal comprising: a transceiver; and a controller coupled with thetransceiver and configured to: obtain first time alignment timer (TAT)information for a first timing advance group (TAG), second TATinformation for a second TAG, and information for configuring asecondary cell (SCell), receive, from a base station, a first mediumaccess control (MAC) control element for activating the SCell, activatethe SCell based on the first MAC control element, receive, from the basestation, a physical downlink control channel (PDCCH) order for the SCellactivated based on the first MAC control element, transmit, to the basestation, a random access preamble based on the PDCCH order, receive,from the base station, a random access response including timing advanceinformation in response to a transmission of the random access preamble,apply the timing advance information to a TAG including the SCell incase that the random access response is received, and start a TATassociated with the TAG including the SCell among the first TATinformation and the second TAT information in case that the randomaccess response is received, wherein the TAT associated with the TAG isused to control how long the terminal considers at least one cellincluded in the TAG to be uplink aligned.
 7. The terminal of claim 6,wherein the controller is further configured to: receive, from the basestation, a second MAC control element including an identity of the TAGincluding the SCell, and a timing advance command (TAC) for the TAGincluding the SCell, apply the TAC to the TAG including the SCell incase that the second MAC control element is received, and restart theTAT associated with the TAG including the SCell among the first TATinformation and the second TAT information in case that the second MACcontrol element is received.
 8. The terminal of claim 7, wherein theidentity of the TAG is set to 0, if the TAG is a primary TAG including aprimary cell (PCell), and wherein the identity of the TAG is set to avalue other than 0 if the TAG is not a primary TAG.
 9. The terminal ofclaim 7, wherein a length of a field of the identity is 2 bits and alength of a field of the TAC is 6 bits.
 10. The terminal of claim 6,wherein the random access preamble is transmitted on the SCell based ona random access channel (RACH) configuration information for the SCell,wherein the random access response is received on a Pcell, and whereinuplink transmission on the SCell is performed based on the timingadvance information.
 11. A method performed by a base station in acommunication system, the method comprising: transmitting, to aterminal, first time alignment timer (TAT) information for a firsttiming advance group (TAG), second TAT information for a second TAG, andinformation for configuring a secondary cell (SCell); transmitting, tothe terminal, a first medium access control (MAC) control element foractivating the SCell; transmitting, to the terminal, a physical downlinkcontrol channel (PDCCH) order for the SCell activated based on the firstMAC control element; receiving, from the terminal, a random accesspreamble in response to the PDCCH order; and transmitting, to theterminal, a random access response including timing advance informationbased on a reception of the random access preamble, wherein the timingadvance information is applied to a TAG including the SCell in responseto the random access response, wherein a TAT associated with the TAGincluding the SCell among the first TAT information and the second TATinformation is started in response to the random access response, andwherein the TAT associated with the TAG is used to control how long theterminal considers at least one cell included in the TAG to be uplinkaligned.
 12. The method of claim 11, further comprising: transmitting,to the terminal, a second MAC control element including an identity ofthe TAG including the SCell, and a timing advance command (TAC) for theTAG including the SCell, wherein the TAC is applied to the TAG includingthe SCell in case that the second MAC control element is received, andwherein the TAT associated with the TAG including the SCell among thefirst TAT information and the second TAT information is restarted incase that the second MAC control element is received.
 13. The method ofclaim 12, wherein the identity of the TAG is set to 0, if the TAG is aprimary TAG including a primary cell (PCell), and wherein the identityof the TAG is set to a value other than 0 if the TAG is not a primaryTAG.
 14. The method of claim 12, wherein a length of a field of theidentity is 2 bits and a length of a field of the TAC is 6 bits.
 15. Themethod of claim 11, wherein the random access preamble is received onthe SCell based on a random access channel (RACH) configurationinformation for the SCell, wherein the random access response istransmitted on a Pcell, and wherein uplink transmission on the SCell isperformed based on the timing advance information.
 16. A base station ina communication system, the base station comprising: a transceiver; anda controller coupled with the transceiver and configured to: transmit,to a terminal, first time alignment timer (TAT) information for a firsttiming advance group (TAG), second TAT information for a second TAG, andinformation for configuring a secondary cell (SCell), transmit, to theterminal, a first medium access control (MAC) control element foractivating the SCell, transmit, to the terminal, a physical downlinkcontrol channel (PDCCH) order for the SCell activated based on the firstMAC control element, receive, from the terminal, a random accesspreamble in response to the PDCCH order, and transmit, to the terminal,a random access response including timing advance information based on areception of the random access preamble, wherein the timing advanceinformation is applied to a TAG including the SCell in response to therandom access response, wherein a TAT associated with the TAG includingthe SCell among the first TAT information and the second TAT informationis started in response to the random access response, and wherein theTAT associated with the TAG is used to control how long the terminalconsiders at least one cell included in the TAG to be uplink aligned.17. The base station of claim 16, wherein the controller is configuredto transmit, to the terminal, a second MAC control element including anidentity of the TAG including the SCell, and a timing advance command(TAC) for the TAG including the SCell, wherein the TAC is applied to theTAG including the SCell in case that the second MAC control element isreceived, and wherein the TAT associated with the TAG including theSCell among the first TAT information and the second TAT information isrestarted in case that the second MAC control element is received. 18.The base station of claim 17, wherein the identity of the TAG is set to0, if the TAG is a primary TAG including a primary cell (PCell), andwherein the identity of the TAG is set to a value other than 0 if theTAG is not a primary TAG.
 19. The base station of claim 17, wherein alength of a field of the identity is 2 bits and a length of a field ofthe TAC is 6 bits.
 20. The base station of claim 16, wherein the randomaccess preamble is received on the SCell based on a random accesschannel (RACH) configuration information for the SCell, wherein therandom access response is transmitted on a Pcell, and wherein uplinktransmission on the SCell is performed based on the timing advanceinformation.